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A new universal definition of myocardial infarction (MI) was unveiled today at the European Society of Cardiology meeting in Munich. The document was developed jointly by the European Society of Cardiology (ESC), the American College of Cardiology (ACC), the American Heart Association (AHA) and the World Heart Federation (WHF) and will be published in five journals: the European Heart Journal, the Journal of the American College of Cardiology, Circulation, Global Heart and Nature Reviews Cardiology. (The document was scheduled to go online on Sunday but is now available, along with extensive support material, on the American Heart Association website.)

The third universal definition of MI establishes the troponin levels required to make a diagnosis of MI in various situations. In a press release, Kristian Thygesen, the co-chair of the document task force, discussed the difficulties the task force encountered in reaching a consensus. Setting a troponin level for procedure-related MIs is difficult “because interventional cardiologists and surgeons do not want myocardial infarction as a complication,” he said. “It means that they want to set the levels of troponin as high as possible. It was also difficult to reach a consensus because it’s impossible to conduct a clinical trial to find the answer.”

The Task Force also expects the new definition will be adopted by the FDA and will be used in clinical trial protocols accepted by the FDA. Said Thygesen, “this is significant because it will help to standardize the way myocardial infarction is defined in clinical trials, making comparisons between trials more meaningful. Steering committees that write protocols for clinical trials do follow FDA requirements.”

The preferred biomarker overall and for each specific category of MI is cardiac troponin (cTn) (I or T), which has high myocardial tissue specificity as well as high clinical sensitivity. An increased cTn concentration is defined as a value exceeding the 99th percentile of a normal reference population (upper reference limit, URL).

Myocardial infarction is determined by the specified cTn value, and at least one of the five following diagnostic criteria:

Symptoms of ischemia

New (or presumably new) significant ST/T wave changes or LBBB

Development of pathological Q waves on ECG

Imaging evidence of new loss of viable myocardium or regional wall motion abnormality